A magnetic storage disk drive system is a digital data storage device that stores digital information within concentric tracks on a storage disk (or platter). The storage disk is coated with a magnetic material that is capable of changing its magnetic orientation in response to an applied magnetic field. During operation of a storage disk drive, the storage disk is rotated about a central axis at a substantially constant rate. To write data to or read data from the storage disk, a magnetic transducer is positioned above a desired track of the storage disk while the storage disk is spinning. Different techniques may be used to move the transducer from a current track to the desired track so that the transducer is properly positioned over the desired track for reading and writing.
Writing is performed by delivering a write signal having a variable current to a transducer while the transducer is held close to the rotating storage disk over the desired track. The write signal creates a variable magnetic field at a gap portion of the transducer that induces magnetic polarity transitions into the desired track. The magnetic polarity transitions are representative of the data being stored.
Reading is performed by sensing magnetic polarity transitions previously written on tracks of the rotating storage disk with the transducer. As the storage disk spins below the transducer, the magnetic polarity transitions on the track present a varying magnetic field to the transducer. The transducer converts the magnetic signal into an analog read signal that is then delivered to a read channel for appropriate processing. The read channel converts the analog read signal into a properly timed digital signal that can be recognized by a host computer system external to disk drive.
The transducer is often dual-purpose, meaning the same transducer can both read from and write to the magnetic storage disk. Combining read and write functions into the same transducer allows some of the structure used for writing also to be used for reading. A dual purpose transducer cannot perform both read and write functions at the same time because, among other reasons: (1) their shared structures generally prohibit use of both functions at one time; and, (2) the magnetic field generated during a write operation tends to saturate the sensitivity of the read element.
Sliders are generally mounted on a gimbaled flexure portion. The gimbaled flexure portion is attached to one end of a suspension's load beam assembly. An opposite end of the suspension's load beam assembly is attached to the in-line rotary voice coil actuator, which provides pivotal motion to slider. A spring biases the load beam and slider with the read/write transducer towards the storage disk, while the air pressure beneath slider developed by storage disk rotation relative to slider pushes slider away from the storage disk. The gimbaled flexure enables slider to present a “flying” attitude toward the storage disk surface and follow its topology. An equilibrium distance defines an “air bearing” and determines the “flying height” of the read/write transducer. Although the separation between the read/write transducer and storage disk created by the air bearing reduces read/write transducer efficiency, the avoidance of direct contact of the transducer with the storage disk vastly improves reliability and extends the useful life of the read/write transducer and storage disk. The air bearing slider and read/write transducer combination is also known as a read/write head/slider assembly or head.
Currently, nominal flying heights are on the order of 0.5 to 2 microinches. For a given read/write transducer, the magnetic storage density increases as the read/write transducer approaches the storage surface of the storage disk. Thus, a very low flying height is traded against transducer reliability over a reasonable service life of the storage disk drive. Increases in data storage densities will require decreases in read/write transducer flying height to near or intermittent contact with a storage surface of the storage disk.
Additionally, the storage disk drive industry has been progressively decreasing both the size and mass of slider structures to reduce the moving mass of the actuator assembly and to permit near or intermittent contact operation of the read/write transducer with the storage disk surface. The former gives rise to improved seek performance and the latter gives rise to improved transducer efficiency and higher aerial density, but at a cost of reduced transducer reliability.
Presently, flight height adjustments occur at using a thermal control mechanism. Unfortunately, the thermal control mechanism exhibits a slow actuation time during thermal flight height adjustment. This is especially important during the write/read and read/write transitions. Current ways to implement a solution to handle the write-read transition issue involve either complex implementation in the firmware or in the sequencer.
One method known as overshoot and undershoot control has a limited use because it is not available during all operating modes. The disadvantage of the old method is that it has to take the current state of the thermal flight height adjustment and write history into account. This requires keeping track of these parameters during the write operation. However, since read and write operations are not allows accessible to the firmware it also requires changes in the hardware components. [I don't understand this last sentence, nor what is intended.]
In a thermally controlled system, the height is principally controlled by a coil heater. When the reading occurs, these systems pull the write head back by a certain amount to allow the thermal protruding to position the write head to a level similar to that occurring during the read operation. Due to the slowness of the thermal response of the device and different time constants between the heater and over the writer coil, the transducer element flight height cannot be set any lower. This limitation, therefore, poses a constraint to further recording densities.
In a multi-headed system, there is the need to switch from one write transducer element to another. To preserve performance, there is the need set the flight height of the transducer element to which control is switching prior to the switching occurring. In other words, there is a need to preheat the target transducer. Otherwise, further degradations in read/write performance occur. When switching from one write transducer element to another, preheating may not be sufficiently rapid to support the switching times for proper multi-head operation.